During some conditions, turbocharged direct-injection engines may generate increased soot. For example, during some conditions, fuel may not sufficiently mix with air before combustion, for example due to reduced turbulence. Such phenomena may occur when the engine is operating at high speed and/or high loads.
The inventors herein have recognized that one approach to address such an issue may be to utilize a particulate filter in the exhaust. However, regeneration of the filter in the exhaust of a spark-ignited engine aimed at stoichoimetric emission control raises numerous issues. As just an example, sufficient excess oxygen for regeneration in the exhaust may result in increased NOx emissions.
As such, systems and methods for controlling regeneration of a particulate filter downstream of an engine in a vehicle are provided herein, including performing particulate filter regeneration during engine shutdown. One exemplary method includes, during an engine shutdown, increasing a throttle opening and regenerating a particulate filter downstream of a three-way catalyst. The method also includes, during an engine start following an engine shutdown, setting one or more engine parameters based on whether the particulate filter was regenerated during a last engine shutdown before the engine start.
By controlling exhaust constituents during an engine start based on whether or not a previous engine shutdown regeneration was carried out, compounds that may have accumulated in the exhaust or in emission control devices during such a previous engine shutdown regeneration can be addressed. For example, increased oxygen may have been stored at an emission control device during a previous engine shutdown regeneration when excess oxygen was being directed to the particulate filter for regeneration. As such, during the engine start, it may be desirable to increase or decrease particular exhaust constituents (e.g., by enriching the combustion air-fuel ratio of a first one or more combustion events from rest) in order to address the stored oxygen or other accumulated compounds.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.